When Sky made its dawn swoop last November to buy 17.9% of ITV, even our usually soporific parliament became twitchy. The Labour MP John Grogan collected 93 signatories to his early day motion (EDM) which noted "with concern" Sky's sudden raid on ITV. Since then until last week, when Richard Branson arrived on the scene to take up the cudgels against Sky in typically combative fashion, both parliament and government have been unusually active. We may just be seeing the start of a public challenge to the media conglomerates.

Last month, another EDM from the Liberal Democrats criticised BSkyB for its misleading advertising to consumers in Whitehaven - about to become the first area in the UK to switch over to digital television. A month ago, following the OFT's provisional finding that Sky's shareholding may give it "material influence" over ITV, another cross-party parliamentary motion asked trade secretary Alistair Darling to order a public interest inquiry from Ofcom. And last Monday, Darling surprised many MPs by doing just that.

On the face of it, a government decision on whether to intervene should have been a no-brainer. How could there not be at least a prima facie case of unacceptable media power than one already dominant player being able, through its shareholdings, to obtain intimate knowledge of a key rival's strategic plans? For those who have dealt corporately with Sky in the past, James Murdoch's reassurances that there would be no "material influence" on ITV drew hollow laughs.

But when it comes to media moguls in general - and the Murdoch dynasty in particular - governments have been notoriously spineless. So while this is only the first skirmish in what is likely to be a drawn-out process, it may just herald a turning-point in parliament's and government's willingness to address the question of overweening media power.

There have been other straws in the wind. Six weeks ago, a small gathering of journalists and politicians at Windsor Castle discussed issues around politics, trust and the media. Even among the journalists present there was some disquiet about untrammelled media excesses, and in particular the lack of any mechanisms of accountability; and tomorrow morning the Culture, Media and Sport select committee will be taking oral evidence as part of its inquiry into press self-regulation.

This is not a sea-change in parliamentary opinion so much as a growing sense of restlessness. MPs are reluctant to legislate on the media for a variety of noble and less noble reasons: not wanting to constrain free speech; fear of antagonising proprietors with the power to swing popular opinion against their party; fear of exposure for indiscretions. But there is a change. Grogan believes it is easier than it was two or three years ago to get his parliamentary colleagues to sign motions on media power, and that Darling's intervention will give MPs more confidence to raise the issue. He also believes that the public interest inquiry is the biggest challenge that Ofcom has faced since its creation. Don Foster, who leads for the Lib Dems on media issues, also believes there is growing concern in parliament about Sky's dominance and "a general mood that this problem needs to be sorted".

Other factors are easing the path to intervention. The almost paranoid fear of Rupert Murdoch's ability to win or lose elections through the influence of his newspapers has faded somewhat as tabloid sales decline and the internet takes hold.

Then there is the arrival of Branson. However furious the objections of ITV or the BBC to perceived regulatory favours conferred on Sky in the past - and there have been many - their arguments never quite cut it. But when Branson rages about Sky's "reckless and cynical attempts to stifle competition and secure creeping control of the British media", he cannot be dismissed as a public servant or failed businessman. Here is another table-thumping, chest-beating business buccaneer who can mix it with the Murdochs on their terms. And if the government finally takes action, it is no longer vulnerable to the traditional News Corporation taunts of being anti-competition or anti-innovation. It is simply promoting a level playing field and protecting pluralism.

We should not get carried away. It is quite possible that Ofcom's inquiry will fizzle out, that Darling will brush away any objections, that the select committee's report on the press and the PCC will be publicly welcomed and privately binned by editors, and that Gordon Brown will sell ITV down the river in order to keep Murdoch onside at the next election. But it is also just possible that something more profound is in the air and that politicians are becoming a little less nervous of the power of media barons, a little more exercised by lack of media accountability, and a little more willing to do something about it.

· Steven Barnett is professor of communications at the University of Westminster